Grusp—Lquatorial Mounting for large Reflecting Telescopes. 257 
4th. It may be objected that currents will be set up in the 
water by the moving of the telescope, which currents will affect 
the steadiness. 
No doubt this will be the case to some extent, but these will 
soon subside, and the motion necessary for following the stars 
will be so slow that no perceptible effect of this kind will be felt 
from it. 
_ As to convenience in getting at the eye-end, there need be no 
difficulty whatever in this form. As the eye-piece is only about | 
15 feet from the centre of motion, the movement of the observer 
is never more than 3 feet per hour. By means of a platform such 
as that shown in fig. 2, running on rails, and quite independent of 
the instrument, the eye end is readily accessible at all times. To 
overcome tbe rotation of the tube as the instrument moves in right 
ascension, I would pierce the tube for eye-pieces every 30° round 
its circumference, and mount the flat mirror and cell in a collar so 
as to enable it to be readily rotated through intervals of 30°. By 
these means the image of the celestial object to be observed could 
be sent through either or any of the perforations of the tube, and 
the observer always observe in the direction most convenient to 
himself. 
